Method of making a fuel cell device assembly and frame

ABSTRACT

An exemplary method of making a fuel cell device assemblies includes the steps of: (i) providing a ceramic batch; (ii) extruding the ceramic batch through a die and a mask to form green extrudate that, in cross-section, has at least 10 cells/in 2  and wall thickness of 50 mils or less; (iii) cutting the green extrudate to an appropriate length to form a green frame blank; (iv) sintering the green frame blank at a temperature of at least 1200° C., preferably at a temperature of between 1400° C. and 1600° C. for at least one hour to form a ceramic frame with a plurality of parallel channels; (v) inserting at least one fuel cell array into its designated position within the ceramic frame; and (vi) sealing the at least one fuel cell array to the frame.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. § 119(e)of U.S. Provisional Application Ser. No. 60/632,041 filed on Nov. 30,2004.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to fuel cell devices, andparticularly to frames for the fuel cell devices.

2. Technical Background

The use of solid oxide fuel cells has been the subject of considerableamount of research in recent years. The typical components of a solidoxide fuel cell (SOFC) comprise a negatively-charged oxygen-ionconducting electrolyte sandwiched between two electrodes. Electricalcurrent is generated in such cells by oxidation, at the anode, of a fuelmaterial, for example hydrogen, which reacts with oxygen ions conductedthrough the electrolyte. Oxygen ions are formed by reduction ofmolecular oxygen at the cathode.

US Patent Publication US2002/0102450 and 2001/0044041 describe solidelectrolyte fuel cells which include an improved electrode-electrolytestructure. This structure comprises a solid electrolyte sheetincorporating a plurality of positive and negative electrodes, bonded toopposite sides of a thin flexible inorganic electrolyte sheet. Oneexample illustrates that the electrodes do not form continuous layers onelectrolyte sheets, but instead define multiple discrete regions orbands. These regions are electronically connected, by means ofelectrical conductors in contact therewith that extend through vias inelectrolyte sheet. The vias are filled with electronically conductivematerials (via interconnects).

U.S. Pat. No. 5,085,455 discloses thin, smooth inorganic sinteredsheets. The disclosed sintered sheets have strength and flexibility topermit bending without breaking as well as excellent stability over awide range of temperatures. Some of the disclosed compositions, such asyttriastabilized zirconia YSZ (Y₂O₃—ZrO₂) would be useful aselectrolytes for fuel cells. It is known that at sufficient temperatures(e.g., about 725° C. and above), zirconia electrolytes exhibit goodionic conductance and very low electronic conductance. U.S. Pat. No.5,273,837 describes the use of such compositions to form thermal shockresistant solid oxide fuel cells.

US Patent Publication US2001/0044043 describes solid electrolyte fuelcells utilizing substantially planar, smooth electrolyte sheet with aroughened interface surface layer. This publication discloseselectrolyte sheet thickness below 45 micrometers. The ceramicelectrolyte sheet is flexible at such thicknesses.

Furthermore, fuel cells endure thermal cycling and large thermalgradients, which induces thermal stresses in the electrolyte sheets. Inaddition, a mounted electrolyte sheet will expand at a rate that isdifferent from the thermal expansion rate of its frame, which may causecracking of the electrolyte sheet. A defect in an electrolyte sheet maynecessitate a replacement of entire cell or electrolyte device.

It is known that substrate type solid oxide fuel cells sometimes utilizemetal alloys as separators. Such configuration is described, forexample, in the article entitled “Electrochemical properties of a SOFCcathode in contact with a chromium-containing alloy separator”, byYoshido Matsuzaki and Isami Yasuda, Solid state Ionics 132 (2000)271-278.

Solid oxide fuel cells may also be supported by a porous supportstructure, as disclosed for example in U.S. Pat. No. 5,486,428. Insidethe porous support structure are sealed corrugated ceramic plates thatform passages for either oxygen or fuel. More specifically, U.S. Pat.No. 5,486,428 discloses fuel cell modules, each having a poroussubstrate supporting a plurality of electrodes. An electrolyte layer issituated over these electrodes and another electrode layer is situatedon the electrolyte layer. The porous support structure forms anintegrated whole with these layers and is inseparable from these layers.The patent discloses that the fuel cell layers are directly bonded tothe porous support structure, therefore fabrication constraints limitfuel cell configuration. For example, the cell layers are generallyfired at different temperatures. Typically the anode and electrolyte aresintered at temperatures of 1400° C. or higher, whereas the cathode isideally sintered at a temperature of 1200° C. or lower. Hence the fuelcell layers must be deposited in decreasing order of firingtemperatures. However, it would be advantageous to be able to have otherdesign configurations of the fuel cell arrays, without concern for thefabrication constraints. Furthermore, the porous support structure isrelatively thick, and therefore, expensive to make. U.S. Pat. No.6,194,095 discloses fuel cell stacks containing fuel cell arrays formedon an electrolyte impregnated porous plastic dielectric sheets with thecell to cell electrical interconnections made through the electrolytemembrane. The disclosed design utilizes air flow manifold units as wellas fuel manifold units assembled between the fuel cell arrays. Havingadditional air and fuel manifold units and assembling them between thefuel cell arrays increases the complexity and the cost of the fuel cellstack.

U.S. Pat. No. 5,416,057 discloses a coated alternating heat exchangerdevice and a method of making such. The heat exchanger comprises aplurality of passages situated within a ceramic body. This patent doesnot disclose the use of this device in fuel cell applications.

SUMMARY OF THE INVENTION

According to one aspect of the invention a method of making a fuel celldevice, said method including the steps of: (i) making a ceramichoneycomb frame having a plurality of parallel channels, the framehaving at least 10 channels/in² and wall thickness of 50 mils or less;and (ii) attaching at least one fuel cell array to said frame.

According to another aspect a method of making a fuel cell deviceincludes the steps of (i) providing a ceramic precursor batch; (ii)extruding the batch through an extrusion die and a mask to form a greenextrudate that, in cross-section, has at least 10 cells/in² and wallthickness of 50 mils or less; (iii) cutting the green extrudate to anappropriate length to form a green frame blank; (iv) sinter the greenframe blank at a temperature of at least 1200° C., preferably at atemperature of between 1400° C. and 1600° C. for at least one hour toform a ceramic frame with a plurality of parallel channels; (v) insertat least one fuel cell array into its designated position within theceramic frame; and (vi) sealing the at least one fuel cell array to theframe.

In another aspect, the present invention includes a method of making aframe for fuel cell arrays, the method comprising the steps of (i)providing a ceramic precorsor batch; (ii) extruding the batch through adie and a mask that has at least 10 openings per square inch to formgreen extrudate that, in cross-section, has at least 10 cells/in² andchannel wall thickness of 50 mils or less; (iii) cutting the greenextrudate to an appropriate length to form a green frame blank; and (iv)sintering the green frame blank at a temperature of at least 1200° C.for at least one hour to form a ceramic frame with a plurality ofparallel channels.

According to some embodiments of the present invention the frame is washcoated with Ni or noble metal catalysts.

Additional features and advantages of the invention will be set forth inthe detailed description which follows, and in part will be readilyapparent to those skilled in the art from that description or recognizedby practicing the invention as described herein, including the detaileddescription which follows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description present embodiments of the invention,and are intended to provide an overview or framework for understandingthe nature and character of the invention as it is claimed. Theaccompanying drawings are included to provide a further understanding ofthe invention, and are incorporated into and constitute a part of thisspecification. The drawings illustrate various embodiments of theinvention, and together with the description serve to explain theprinciples and operations of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a cross-sectional view of oneembodiment of the present invention;

FIGS. 2A-2C are cross-sectional schematic views the portions ofdifferent frames for supporting fuel cell arrays, such as thatillustrated in FIG. 1.

FIG. 3A is a cross sectional schematic view of a honeycomb frame and twofuel cell arrays bonded thereon.

FIG. 3B illustrates schematically a planar view of the honeycomb frameand the fuel cell arrays shown in FIG. 3A.

FIGS. 4A and 4B illustrate schematically a fuel cell module, including ahoneycomb frame with internal heat exchange.

FIGS. 5A and 5B illustrate schematically a fuel cell device assemblycomprising a fuel cell stack with joined honeycomb frames.

FIGS. 6A and 6B illustrate schematically a fuel cell device assemblythat includes a honeycomb frame that has additional cross supportsurfaces.

FIGS. 7A and 7B illustrate schematically a fuel cell device assemblythat includes a honeycomb frame with reciprocating gas flow.

FIGS. 8A and 8B is a schematic illustration of another embodiment of thefuel cell device assembly that includes a honeycomb frame.

FIG. 9 is a schematic illustration of the fuel cell device assembly thatincludes two fuel cell modules.

FIG. 10 is a schematic diagram illustrating one method for making aframe for the fuel cell device assembly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the present preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings. Whenever possible, the same reference numeralswill be used throughout the drawings to refer to the same or like parts.One embodiment of the fuel cell device includes: (i) at least oneelectrolyte sheet; (ii) a plurality of cathodes disposed on one side ofthe electrolyte sheet; (iii) a plurality of anodes disposed on anotherside of the electrolyte sheet; and (iv) a frame supporting theelectrolyte sheet, the frame having a plurality of parallel channels.The channels may be utilized to provide the required reactant to theanodes and/or cathodes. It is preferable that a cross-sectional area ofthe frame has a channel density of at least 10 per in², more preferablyat least 20 per in², and most preferably at least 100 per in². It ispreferable that channel wall thickness is 50 mils or less, morepreferably 30, most preferably 20 or less. It is preferable that theframe 50 include at least 20 channels.

The fuel cell device may further include a second electrolyte sheetattached to the frame, where the second electrolyte sheet also supportsa plurality of cathodes and anodes situated on opposing sides of thissecond electrolyte sheet. The two electrolyte sheets are oriented suchthat either (i) anodes situated on the first electrolyte sheet faceanodes situated on the second electrolyte sheet, or (ii) cathodessituated on the first electrolyte sheet face cathodes situated on thesecond electrolyte sheet, to enable reactant flow through the frame andbetween the electrolyte sheets.

One embodiment of the present invention is shown in FIG. 1, and isdesignated generally throughout by the reference numeral 10. Inaccordance with this embodiment of the present invention the fuel celldevice assembly 10 includes: (i) at least one fuel cell array 15including an electrolyte sheet 20; a plurality of cathodes 30 disposedon one side of the electrolyte sheet 20 and a plurality of anodes 40disposed on another side of the electrolyte sheet 20; and (ii) a frame50 supporting the electrolyte sheet 20. The anodes 40 and cathodes 30are interconnected by via interconnects 35 that extend through via holesin the electrolyte sheets The frame 50 has a plurality of channels 52surrounded by solid walls 54. The frame 50 is preferably a honeycombframe. That is, it has a “cellular” structure with highstrength-to-weight ratio due to thin cellular walls, and the cell'scross-sections are preferably hexagonal, rectangular, square, orcircular. FIGS. 2A-2C Illustrate some of the frame cell geometries. Thecross-sections are shown normal to the cross-section of the frame 50illustrated in FIG. 1. It is preferable that the frame 50 have ahoneycomb structure. It is also preferable that the frame 50 have CTEclose to that of electrolyte sheet 20, in order to provide expansion,comparable to that of the electrolyte sheet 20. If the electrolyte sheet20 is made of partially stabilized zirconia (e.g., 3YSZ), it ispreferable that the frame 50 has CTE (CTE=ΔL/LΔT) of about 9 to 13 ppm/°C. and preferably 10 to 12 ppm/° C. Such CTE's may be realized forexample, with ceramic compositions within the magnesia (MgO)—spinel(MgAl₂O₄) system.

Making the frame 50 with multiple channels 52 provides the advantage ofhaving a multiple channels for reactant flow, while reducing the framedensity and increasing the surface area due to its high OFA (openfrontal area). The term “open frontal area” refers to the geometricfraction of the cross-sectional area of the frame 50 that is not filledby the solid materials (walls). It is preferable that OFA be higher than0.4 and even more preferable that OFA be higher than 0.5. It ispreferable that the geometrical wall surface area (GSA) of the frame 50be higher than 5, more preferably higher than 10 and most preferablethat GSA be between 15 and 100. Table 1 provides some examples ofhoneycomb frame geometries. In this table, the ratio ρ_(hc)/ρ_(solid)denotes the ratio of “apparent” or effective honeycomb frame densityrelative to the density of the frame if it was made only from the solidmaterial. For example, Table 1 shows that the frame 50 with cell densityof 900 per in² and the wall thickness of 2 mils (0.05 mm) will be only0.12 as dense as if it was made of the same solid materials, whilehaving a large geometrical surface area GSA of 44.4 and OFA of 0.88.TABLE 1 Wall Wall Cell density Thickness Thickness ρ_(hc)/ GSA(cells/in²) (mils) (mm) OFA ρ_(solid) (cm²/cm³) 200 16 0.41 0.55 0.4517.2 400 8 0.3 0.68 0.32 26.5 400 6 0.15 0.76 0.24 27.7 400 4 0.10 0.840.16 29.0 600 4 0.10 0.80 0.20 34.8 900 2 0.05 0.88 0.12 44.4

As can be seen from the examples depicted in Table 1, thecross-sectional area of the frame 50 has channel (cell) density of atleast 20 cells/in². It is preferable that the channel density be atleast 50 cells/in², and most preferably at least 100 cells/in² andchannel wall thickness be 20 mils or less. One advantage of the frame 50is that because of the thin channel walls and/or high GSA relative tothe frame made of only solid material, frame 50 has low thermal massrelative to a similar frame made from a solid material and thus canwithstand faster thermal cycling rates than a similar frame made of onlysolid material. Furthermore, the channels 52 may be utilized tofacilitate heat exchange within the frame 50. Finally, because frame 50has a large surface area, the channel surfaces may be utilized forefficient catalyst dispersion.

It is preferable that frame 50 be ceramic. For ceramic materials, underconditions of low Blot modulus, the thermoplastic result (realistic heattransfer rates) for maximum stress is:σ=(αEΔThl)/{k(1−μ)}where α is the thermal expansion coefficient, E is Young's modulus, ΔTthe surface temperature change, h the heat transfer rate, l acharacteristic dimension, k thermal conductivity, and μ Poisson's ratio.The maximum stress is directly proportional to characteristic dimensionl. Considering the case where a gas flows uniformly through the channels52 of the honeycomb frame 50 and the temperature and rate of gas flowdetermine the heat transfer rate to/from the walls of the honeycombstructure, the characteristic dimension is the wall thickness. For asolid frame under similar conditions, the characteristic dimension isthe width or height of the frame, which is expected to be severalmillimeters or centimeters wide (high). Comparing the wall thickness ofcommon honeycomb geometries (listed in Table 1) indicates that theframes 50 with the honeycomb structure will have the stress reduced(compared to a solid frame) by approximately one to two orders ofmagnitude due to the significantly thinner heated dimensions (channelwalls).

A sealant 60 bonds the electrolyte sheet 20 to the frame 50. It ispreferable that the sealant 60 be a hermetic sealant, for example a fritglass seal or a metal braze. Other hermetic sealants may also be used.The frame 50 may also contain exhaust openings 85, 85′ where it iscollected for additional thermal management and/or fuel recycling

EXAMPLES

The invention will be further clarified by the following examples.

Example 1

One exemplary fuel cell device assembly according to the presentinvention is illustrated schematically in FIGS. 3A and 3B. FIG. 3A is aschematic cross-sectional view of an exemplary fuel cell device assembly10. FIG. 3B is a schematic illustration of the top (planar) view of fuelcell device assembly illustrated in FIG. 3A. The direction of reactant(e.g., fuel) flow within the fuel cell device assembly is indicated bythe arrows.

As shown in these figures, a fuel cell array assembly 10 comprises onefuel cell module 12. The fuel cell module 12 includes the frame 50 thatsupports two parallel fuel cell arrays 15, oriented such that the twosets of electrodes (e.g., anodes 40) face one another, forming areactant (e.g., anode) chamber 80 therebetween. The frame 50 is bondedto the fuel cell arrays 15 by sealant 60. Fuel, for use with the fuelcell device assembly 10, is fed towards the frame 50, for example,through a gas distributing end piece 70 which is sealed to the frame 50with a sealant 60′. The fuel passes (see direction of arrows) from theend piece 70, through the flow channels 52, to the anode chamber 80formed by the two electrolyte sheets, into the exhaust flow channels52′, and is then exhausted via exhaust apertures 85. In this embodimentthe exhaust apertures 85 are located on the section of the frame 50Bsituated furthest from the end piece 70 (exhaust side).

Thus, according to an embodiment of a present invention, a fuel celldevice assembly 10 has a fuel cell stack that includes: (i) at least twofuel cell arrays 15, each fuel cell array 15 having a plurality ofinterconnected cathodes and anodes 30, 40 situated on opposite sides ofan electrolyte sheet 20; and (ii) a frame 50 supporting the fuel cellarrays 15, such that the fuel cell arrays 15 are separated from oneanother and form at least one chamber (e.g., anode chamber 80)therebetween. The total number of chambers will depend on a total numberof the fuel cells arrays 15 in a fuel cell stack. Thus, the fuel cellstack may include one or more modules 12. As defined herein, a fuel cellmodule 12 is two fuel cell arrays 15 bonded to the frame 50 and theassociated electrical connector(s) between the two fuel cell arrays. Theframe(s) 50 has a plurality of flow channels 52, to enable reactants(e.g. fuel) to flow through the frame(s) 50 and through the reactantchamber(s) 80 and/or 80′. In this embodiment, the fuel enters the anodechamber(s) 80 through the flow channels 52 and contacts anodes 40 of thefuel cell arrays 15. The exhaust fuel continues to flow through theexhaust flow channels 52 of frame 50, in the same direction, until it iscollected from the exhaust openings 85. FIGS. 3A and 3B illustrate thatflow channels 52 are situated in frame section 50A, while the exhaustflow channels 52′ are situated in the frame section 50B. The fuel stackassembly is allayed in an air chamber 83, which contains air inletaperture(s) 84 connected to the air inlet tube(s) 88 and air exhaustaperture(s) 84′ connected to the air exhaust tube(s) 88′. The airchamber 83 provides air or oxygen to the cathodes 30 to enable operationof the fuel cells. This is shown schematically in FIGS. 3A and 3B.

Example 2

FIGS. 4A and 4B illustrate another embodiment of the present invention.FIG. 4A is a schematic cross-sectional view of the exemplary fuel celldevice assembly providing heat exchange. FIG. 4B is a schematicillustration of the top (planar) view of the fuel cell device assemblyillustrated in FIG. 4A.

In this embodiment the frame 50 is a heat exchanger. The frame 50supports two parallel fuel cell arrays 15, oriented such that the twosets of anodes 40 face one another, forming anode chambers 80therebetween. The anode chambers 80 are separated from one another bythe heat exchange channel flow portion 80A of the central fuel flowchannel(s) 52. According to this embodiment, the frame 50 includes atleast one inlet opening 51 coupled to a fuel distribution end piece 70and at least one exhaust outlet 85′ located on the side of the frameattached to the fuel distribution end piece 70 (i.e. frame section 50A).At least one plug 86 prevents the fuel from exiting the central flowchannel(s) 52 as it is done in the previous example. The fuel (asindicated by arrows in FIG. 4A) moves through the central flowchannel(s) 52 and enters the heat exchange flow channel portion 80A.While moving through the heat exchange flow channel portion 80A the gasfuel is heated, via heat exchange (through channel walls 54) with theanode chambers 80. The heated gas fuel continues to flow through thecentral flow channel(s) 52 and is redirected via turnaround apertures 87to the peripheral fuel flow channels 52 (section 50B of the frame) fromwhich it enters into the anode chambers 80 where it is distributedacross the anodes 40. That is, fuel gas exits (central) fuel flowchannels 52 through the aperture(s) 87 in the channel wall(s) 54 andflows counter to its previous direction inside the peripheral channels52, from which it enters the anode chambers 80. The gas fuel heats as itmoves across the anodes 40 in the anode chamber 80 and the hot exhaustfuel enters the exhaust fuel channel(s) 52′ (section 50A of the frame).Thus, in this embodiment the initial fuel flow moves in reversedirection to the exhaust fuel flow. As stated above, when the fuel movesacross the electrodes of each cell, it gets hotter and hotter. It issignificantly hotter when it re-enters section 50A of the frame, than itwas when it entered the frame section 50A through the fuel inlet 51. Thehot exhaust fuel enters the exhaust flow channels 52′ and moves counterto the fuel flow within central channels 52. The direction of fuelthrough the peripheral channels 52, 52′ is illustrated schematically byarrows in FIG. 4B. When the hot exhaust fuel enters section 50A of theframe 50, heat is transferred from channels 52′ to the central channels52 through the walls 54, thereby cooling down the exhaust flow channels52′ and heating the incoming fuel. Thus, the frame 50 of this embodimentacts as a heat exchanger. The frame 50 shown in FIG. 4A-4B includes aplurality of fuel flow channels 52 and a plurality of separate exhaustfuel flow channels 52′, both situated in frame sections 50A.

As in a previous example, the fuel cell stack assembly is allayed in theair chamber 83, which contains air inlet aperture(s) 84 connected to theair inlet tube(s) 88 and air exhaust aperture(s) 84′ connected to theair exhaust tube(s) 88′. The air chamber 83 provides air or oxygen tothe cathodes 30 to enable operation of the fuel cells. The air chamber83 is shown schematically in FIGS. 4A and 4B.

Example 3

As shown in FIGS. 5A and 5B, the fuel cell stack may include three ormore fuel cell arrays 15 supported by the frame(s) 50, such that (i)anode sides of at least two of the fuel cell arrays 15 face each other,thereby forming an anode chamber 80 and (ii) cathode sides of at leasttwo of the fuel cell arrays 15 also face one another, thereby forming acathode chamber 80′. As shown in FIG. 5B, frames 50 have a plurality ofparallel channels 52 providing (a) fuel gas to the anode chamber 80 and(b) oxygen flow to the cathode chamber 80′. The frames 50 also have aplurality of channels 52′ for the exhaust gases to exit thecathode/anode chambers 80′, 80. As described in the prior examples, thefuel cell arrays 15 are bonded to the frames 50 with a sealant 60. A“packet” type fuel cell stack is formed by utilizing frame(s) 50 andmultiple fuel cell arrays to form reactant chambers (packets)therebetween.

Thus, as shown in FIGS. 5A and 5B, an exemplary fuel cell deviceassembly 10 includes: (I) a plurality of electrically interconnectedfuel cell arrays 15, each including: an electrolyte sheet 20; a set ofelectrodes, the first set of electrodes being a plurality of cathodes 30disposed on one side of the electrolyte sheet 20; a second set ofelectrodes, the second set of electrodes being a plurality of anodes 40disposed on another side of the electrolyte sheet 20; and (II) frames 50supporting and attached to the electrolyte sheets 20, the frame 50having a plurality of parallel channels 52 for providing a reactant toat least one set of the electrodes. A frame 51 separates the frames 50which are banded to electrolyte sheet 20. Frame 151 may be sealed toframes 50 with seal 161. It is preferable that the frame cross-sectionalarea of the frame 50 has channel density of at least 10 channels/in² andpreferably at least 50 channels/in² and channel wall thickness of 20mils or less. It is most preferable that the channel density be at least100 channels/in². The plurality of the electrolyte sheets 20 areoriented such that (i) anodes 40 situated on the one of the electrolytesheets face anodes 40 situated on another one of the electrolyte sheets,to enable reactant flow through the frames 50 and between the fuel cellarrays 15; and (ii) cathodes 30 situated on one of the electrolytesheets face cathodes 30 situated on the yet another one of theelectrolyte sheets, thus forming an oxygen (cathode) chamber 80′.Preferably the air or oxygen gas flows through the frame(s) 151, viachannels 153, into the oxygen chamber, comes into contact with thecathodes and then flows through the frame(s) 151, via channels 153′ andout of the frame's exhaust apertures 85. In this embodiment, theexhausted fuel and air are provided to the combustion chamber 91 wherethe exhausted fuel burns. The resultant heat from the combustion chamberis provided, as needed, to the fuel cell device assembly to enable amore efficient operation.

Example 4

A number of variations or modifications to the basic honeycomb frameconcept described above can be made to implement different stackconfigurations. One such variation includes frame 50 that includesperiodic support structure(s) 50′, which provide additional surfaces forsupport of the planar fuel cell arrays 15. As shown in FIG. 6A, the fuelcell device assembly 10 may include more than one column of the fuelcell arrays 15. The fuel cell arrays 15 are bonded to the frame 50 atouter edges, as well as to the support structure(s) 50′, with sealant60. The fuel cell arrays 15 are situated such that the anodes 40 facethe internal anode chamber 80. Alternatively, it is sometimes desirableto allow fuel cell arrays flexural freedom, but to limit deflection. Onemeans of limiting deflection but allowing flexural deformation fuel cellarrays 15 is to provide a frame 50 and support structure(s) 50′, asillustrated in FIG. 6A, but to eliminate the sealant 60 joining the fuelcell array 15 to the support structure 50′. This is shown in FIG. 6B.

Example 5

The support structures 50′ may also provide a gas distribution function.FIGS. 7A and 7B illustrate schematically a fuel cell device assembly 10that utilizes frame 50 for reciprocating distribution of the fuel flow.Such frames 50 advantageously achieve greater fuel utilization andgreater thermal uniformity. Frame 50 has a honeycomb structure andincludes support structures 50′ and 50″ situated within the anodechamber 80. Some of the honeycomb channels 52 of the frame section 50Aare plugged near the fuel inlet end with a plug 53, thereby directinginlet fuel through channels in part 50A′ of the section 50A. The part50A′ of the section 50A is located between one edge of the frame 50 andthe edge of support structure 50′. Similarly near the fuel exhaust end,frame section 50B is plugged with a plug 53, restricting fuel exhaust toonly some of the channels 52′. The support structures 50′ and 50″ haveopenings 85″ with respect to the perimeter portion of the frame 50 whichguide the fuel gas flow in a reciprocating fashion (as shown by arrows)until it exits into exhaust intake 70′. The serpentine movement of thefuel gas across the electrodes provides a longer path length for thefuel and thus achieves better fuel utilization as well as greaterthermal uniformity across the fuel cell arrays 15.

Example 6

The ability to separate manufacturing of the fuel cell arrays 15 fromthe manufacturing of the frame 50 enables greater design flexibility.For example, because manufacturing of the frame and the manufacturing ofthe fuel cell array are two separate processes, different orientationsof the electrodes with respect to the frame cavity are now possible. Oneembodiment of the present invention is illustrated in FIGS. 8A and 8B.In this embodiment the fuel cell arrays 15 are bonded to frame 50 withthe cathode side facing the interior of the frame 50. In thiscathode-facing-cathode arrangement, air is supplied through the parallelchannels 52 of the honeycomb frame 50 to the interior cathode chambers80′ while fuel for the anodes is supplied outside of these chambers, onthe anode facing sides of the fuel cell arrays 15. More specifically,air is fed through the air inlet 90 and enters the fuel cell air inletcentral channels 52. A turnaround at or near the end of the fuel cellair inlet channels 52, distributes air from the air inlet channels tothe peripheral channels 52 which supply air to the cathodes 30. Theexhausted air is directed out through the air exhaust aperture 85.

FIGS. 8A and 8B illustrate that the housing 100 forms the fueldistribution chamber 102. The Frame 50 and the fuel cell arrays 15bonded thereto are situated inside chamber 102, such that fuel is incontact with the anodes 40 of the fuel cell arrays 15. The housing 100has at least one, and preferably a plurality of fuel gas inlets 112which are connected to the fuel distributor 105. Fuel is exhausted fromthe chamber 102 through one or more fuel gas exhaust aperture 107situated in the housing 100. The exhausted fuel and air may be combinedin a combustion chamber to generate heat, which can then be utilized bythe fuel stack to warm up the incoming fuel to the desired temperature.The fuel cell device assembly 10 illustrated in FIGS. 8A and 8B has anadvantage of improved thermo-mechanical durability because the frame 50and the attached fuel cell arrays 15 (i.e., fuel cell modules) aremechanically fixed to the housing 100 by a seal 115 only at one end ofthe module. As illustrated in these figures, the frame 50 and theattached fuel cell arrays 15 are supported by the inlet side seal 115between the housing 100 and the modules 12.

However, in an alternative arrangement, the frame 50 and the attachedfuel cell arrays 15 may rest on a compliant support 120 (shownschematically in FIG. 8A by dashed lines). The compliant support 120 maybe, for example, metal foam situated inside the chamber 102.

Since the frame 50 and the attached fuel cell array(s) 15 are not heldin a fixed position near the opposite end (the air turnaround) of thehousing 100, excessive strain from thermal gradients across the lengthof the module are either minimized or avoided altogether. A firstelectrical connection 125 to the first fuel cell array 15 may be madewith a solid conductor such as Ni or Ag wire or Ni or Ag ribbon attachedto the cathode contact 130. The anode contact pad 130 is made, foeexample, of silver-palladium alloy (silver-palladium cermet). The anodecontact pad 130 is connected through a via interconnect to a firstcathode 30. A second electrical connection, between the two fuel cellarrays 15 shown in these figures, may also include solid conductor 140such as Ag or Ni wire or Ag or Ni ribbon attached to the anode 40portion of the first array and the cathode contact 130 of the secondarray 15, routed along the periphery of the frame 50. A third electricalconnection 142, to the second fuel cell array 15, may include solidconductor such as Ag or Ni wire or Ag or Ni ribbon attached to the lastanode 40 of the second fuel cell array 15. The first and thirdelectrical connections 125, 142 may then be extended through the housing100 to enable wiring of multiple devices 10 and power extraction.

Example 7

FIG. 9 illustrates schematically another embodiment of the fuel celldevice assembly 10. This embodiment is similar to that illustrated inFIGS. 8A and 8B, but includes two fuel cell modules 12 (i.e. two sets offrames 50, with each frame supporting two fuel cell arrays 15). Thisarrangement has the advantage multiple modules can share a commonhousing 100, which provides a compact design with good fuel utilization.Module to module electrical interconnection 143 can be provided by aninexpensive base metal such as a nickel screen, felt or mesh becausethis interconnection is situated in the fuel chamber, and not in theoxidizing environment. Any number of the interconnected modules may beplaced in the gas distribution chamber 102, as needed. Morespecifically, FIG. 9 illustrates that two fuel cell modules 12 (eachwith two multicell planar fuel cell arrays 15 bonded to either side ofthe frame 50) are situated inside a gas distribution chamber 102 formedby the housing 100. The housing 100 contains a fuel distribution plate145 and has through holes 112 which allow for distribution of the fuelthat enters fuel cell assembly 10 through the fuel inlet 150. Fuel isexhausted through a narrow slit 185 in plate 155 of the housing 100 andenters from the chamber 102 into combustion chamber 160. Plate 155separates the combustion chamber 160 from the fuel chamber 102. Air isfed through inlet 165 and enters the fuel cell modules 12 through flowchannels 52 of the frame(s) 50. A seal 171 reduces fresh air incursioninto the combustion chamber 160. The air distribution geometry, thoughnot illustrated here, is similar to that illustrated in FIGS. 8A and 8B.A turnaround at the bottom end of the honeycomb distributes the air frominterior inlet channels of the honeycomb to perimeter channels whichsupply the cells. Ultimately air is exhausted through exhaust slits 170.The exhausted air mixes with exhausted fuel, providing a combustionproduct exhausted through the combustion exhaust 175.

Electrical interconnection 143 between the two fuel cells modules 12 isprovided, for example, by a compliant nickel felt, which is bonded tothe cathode contact 130, in a manner similar to that of the thirdelectrical connection 142 illustrated in FIG. 8A, and to the top anode40 of the adjacent module 15. Electrical contact between two fuel cellarrays 15 of each fuel cell module 12 can be provided in a mannersimilar to that illustrated in FIG. 8A.

Other Advantages Provided by the Frame

The high geometric surface area provided by the walls of the honeycombframe 50 is beneficial for distributing fuel reforming catalyst material(for example, Ni metal or noble metals) for converting hydrocarbon (gas)fuel into a hydrogen rich gas stream. This provides excellent access ofthe reactant gas to the catalyst material at low backpressure (i.e., lowpressure drop between inlet aperture pressure and the exhaust aperturepressure), for example, below 1 PSI. Therefore, it is advantageous tointegrate catalytic functionality within the honeycomb frame 50. Forsolid oxide fuel cells (SOFC) illustrated, for example those illustratedin the above described figures, channels 52 in the frame section(s) 50A,situated upstream from the anode chamber 80, may be catalyzed to providefuel reformation. Catalyzation of the channel walls 54 may be achievedby wash coating (for example, by wash coating, via immersion of theporous portions of the channel walls 54 of the frame 50 in a slurry ofhigh-surface area ceramic particles (e.g. high surface area alumina)with Ni or noble metal catalysts carried on the surfaces of the ceramicparticles). In order to provide catalytic oxidation, noble metalcatalysts may be deposited (for example, by wash coating as describedabove, onto the channel walls 54 in the porous portions of frame 50) atthe exhaust end of the frame 50. This will enable lean spentfuel/oxidant mixtures to efficiently combust and improve heat exchangeefficiency. The resultant heat may be utilized, for example, to heat(via heat exchanger) the incoming gas fuel to the operating temperaturerequired by the fuel cells (e.g., about 700° C.), to provide moreefficient operation of the fuel cell stack assembly.

In certain situations the channel walls 54 may be too dense (not porousenough) for effective wash coating. In this case, the catalyst may beincorporated into the wall 54 by inclusion in the forming process. Forexample, Ni reforming catalyst may be included by adding NiO into theframe precursor materials. The NiO will, on reduction by the fuel gas,form distributed Ni fuel reformation catalyst at the surface of the flowchannels 52. Preferably, the NiO component should be less than 30 volumepercent of the inorganic material to avoid loss of structural integrityin the finished frame. More preferably the NiO component should be 10%or less. As stated above, for certain applications (including, but notlimited to combined cycle systems), it may be beneficial to catalyze thechannel walls 54 in the frame section 50B, located near the exhaustapertures 85, with an oxidation catalyst by including the noble metal(s)into frame forming materials, which on reduction will form distributednoble metal oxidation catalyst at the surface of the flow channels 52.This will enable the fuel cell assembly to efficiently utilize unreactedfuel to produce thermal energy.

The flow channels 52, 52′ may also be used as insulating conduits forlead wires, or sensor (e.g. thermocouple) wires. Some of the channels52, 52′ may be dedicated for running leads and/or sensor wires tovarious locations on the planar array fuel cell. The channels provide alow cost alternative for containing and supporting wires which requireinsulation.

The “self-contained” nature of a honeycomb/planar fuel cell arrayassembly enables other beneficial design approaches. Since “long”honeycomb frames may be easily manufactured, different sections of theframe 50 may be maintained at different temperatures. One may wish, forexample, to maintain the inlet to the frame 50 at lowtemperature—enabling the use of a low-temperature polymer seal 60between the inlet manifold and the frame 50

As embodied herein and depicted in FIG. 10 the frame 50 may be made of3YSZ and the fuel cell device assembly may be manufactured, for example,by utilizing the extrusion process for making a frame and attaching fuelcell array(s) according to the following steps:

1. Provide a ceramic precursor batch, for example batch containing 3YSZpowder with polymer binders and lubricants;

2. Extrude the ceramic batch through a die and the mask that has atleast 10 openings per square inch to form green extrudate that, incross-section, has at least 10 cells/in² and wall thickness of 50 milsor less.

3. Cut the green extrudate to an appropriate length to form a greenframe blank. At this point one or more sections in the green frame blankmay be cut away to form a place for holding at least one fuel cellarray. The size of the opening should be larger than the size of thefuel cell array by the amount of anticipated shrinkage during sintering.

5. Sinter the resultant green frame at a temperature of at least 1200°C., preferably at a temperature of between 1400° C. and 1600° C. for atleast one hour to form a ceramic frame 50 with a plurality of parallelchannels.

6. Cool the frame. If the green frame was not cut to create place forone or more electrolyte sheets, the cooled frame may be machined tocreate at least one receptacles for one or more fuel cell arrays 15.

7. Insert the fuel cell array(s) 15 into its designated position(s).

8. Seal the fuel cell array(s) 15 to the frame 50.

EXAMPLE

-   1. An extrusion batch of 3YSZ with 3% by weight methlycellulose as    the binder is mixed with water to a consistency appropriate for    extrusion.-   2. The batch is ram extruded through die, for example a 200 cell per    square in die with 16 mil spacing between the pins. A rectangular    mask is placed in front of the die to form a “200/16” green    extrudate comprising a rectangular array of channels with four    horizontal “rows” and seventeen vertical “columns.”-   3. Parts are cut to just over 32″ in the green state. In the middle    of the part an opening 1.5″ long and 0.75″ wide (corresponding to 11    channels) is cut halfway through the extrudate (two channels deep)    to create an anode chamber.-   4. In order to seal a small number of defects in the exterior skin,    the external surface is painted with a 3YSZ slip. Details of the    exemplary 3YSZ slip composition and fabrication may be found in U.S.    Pat. No. 6,623,881, incorporated by reference herein. Additionally,    the YSZ slip is used to plug the bottom two rows of channels to    provide an exhaust restriction to prevent air incursion into the    anode chamber.-   5. The green part is sintered at approximately 1450° C. After    sintering for four hours, the green part shrinks linearly    approximately 25% and has front face dimensions of ¼″×1″ and a    length of 24″

An aluminum metal end-piece which distributes the inlet gas from a ¼″stainless steel tube to the frame's channels was sealed to the extrudatetube using an organic epoxy.

A single cell test piece with LSM/YSZ cathode and a Ni/YSZ anode andAg—Pd alloy current collectors is screen printed and fired on a 20 umthick 3YSZ electrolyte sheet with dimensions 1″×2″. Via interconnectsare used to allow the anode electrical lead contact to be made on theair side. The test piece is sealed to the 3YSZ extrudate frame using aAg—Pd alloy. Silver lead wires were bonded to Ag—Pd alloy contact padscontacting the cell using a Ag—Pd ink. Upon testing at 725° C. underhydrogen bubbled through water, open circuit voltage of just over 1V wasmeasured, indicating minimal cross-over leakage.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the present inventionwithout departing from the spirit and scope of the invention. Thus it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A method of making a fuel cell device, said method including thesteps of: (i) making a ceramic honeycomb frame having a plurality ofparallel channels, the frame having at least 10 channels/in² and wallthickness of 50 mils or less; and (ii) attaching at least two fuel cellarray to said frame.
 2. A method of making a fuel cell device, saidmethod including the steps of (i) providing a ceramic batch; (ii)extruding the ceramic batch through a die and a mask to form greenextrudate that, in cross-section, has at least 10 cells/in² and wallthickness of 50 mils or less; (iii) cutting the green extrudate to anappropriate length to form a green frame blank; (iv) sintering the greenframe blank at a temperature of at least 1200° C., preferably at atemperature of between 1400° C. and 1600° C. for at least one hour toform a ceramic frame with a plurality of parallel channels; (v)inserting at least one fuel cell array into its designated positionwithin the ceramic frame; and (vi) sealing the at least one fuel cellarray to the frame.
 3. The method of making a fuel cell device accordingto claim 2, further including the step of cutting out one or moresections in the green frame blank to form a place for holding at leastone fuel cell array.
 4. A method of making a frame for fuel cell arrays,said method comprising the steps of (i) providing a ceramic batch; (ii)extruding the ceramic batch through a die and a mask that has at least10 openings per square inch, to form green extrudate that, incross-section, has at least 10 cells/in² and channel wall thickness of50 mils or less; (iii) cutting the green extrudate to an appropriatelength to form a green frame blank; and (iv) sintering the green frameblank at a temperature of at least 1200° C. for at least one hour toform a ceramic frame with a plurality of parallel channels.
 5. Themethod of making a frame for fuel cell arrays according to claim 4,including the step of wash coating at least some sections of frame'schannel walls by wash coating with Ni or noble metal catalysts.
 6. Themethod of making a frame for fuel cell arrays according to claim 5wherein the step of wash coating includes immersion of the porousportions of the channel walls of the frame in a slurry of high-surfacearea ceramic particles with Ni or noble metal catalysts carried on thesurfaces of the ceramic particles.
 7. The method of making a frame forfuel cell arrays according to claim 4 including the step of adding NiOinto ceramic slip.
 8. The method of making a frame for fuel cell arraysaccording to claim 7, wherein the ceramic slip includes NiO and theamount of NiO is less than 30 percent of volume of the total inorganicmaterial comprising the slip.
 9. The method of making a frame for fuelcell arrays according to claim 8 wherein the amount of NiO is less than10 percent of valume of the total inorganic material comprising theslip.